This invention relates to a method of making a semiconductor device, especially to a method of forming a film of a resin on the surface of a semiconductor body for stabilizing the surface of the semiconductor device.
Heretofore, a silicon dioxide film has been most frequently used for passivating p-n junctions of a semiconductor element.
A relatively thick silicon dioxide film is required for attaining the above property, however, it is difficult to form films of the required thickness because a length of time required for forming them. Moreover, even if a film of required thickness is obtained, cracks inherently appear in the film owing to the differences of expansion coefficients between silicon and silicon dioxide.
In order to obtain the silicon dioxide film, a silicon body has to be heated at a temperature of about 1000.degree. to 1200.degree. C, and hence the use of a heat source of a large scale and other equipment are indispensable. Other methods for forming a silicon dioxide film at relatively low temperatures have been proposed such as a Chemical Vapor Deposition method (CVD method) or sputtering method. But, films of uneven thickness or porous films are likely to be obtained by these methods.
For overcoming these defects as mentioned above, silicone rubbers or silicone resins are utilized for forming a film for stabilizing a surface of a semiconductor body. By using these materials, a film with a high voltage resistance and with a large thickness, e.g., up to about 100.mu. or more, may be obtained at a relatively low treatment temperature. However the leakage resistance of such films is small, and the heat resistance, adhesion, and thermal shock resistance of the films are generally insufficient.
For these reasons, silicone rubber or silicone resin films are not applied for a semiconductor device requiring a high efficiency.
Recently, the use of a film of polyimide resin or polyamideimide resin with good electric properties has been proposed. For forming films of these resins, a semiconductor body has to be heated to a relatively high temperature, e.g., about 250.degree. C or above, which damages electrodes or leadwires when electrodes or leadwires are previously fitted, or which requires additional complicated steps such as photoetching when electrodes or leadwires are fitted as a final stage.
An object of the invention is to provide a method of making a semiconductor device with a fewer steps.
Another object of the present invention is to provide a method of making a semiconductor device suitable for mass production.
A further object of the present invention is to provide a method for forming a film for stabilizing the surface of a semiconductor body at a relatively low temperature.
A further object of the present invention is to provide a method of making a semiconductor device using an improved coating material of high thermal shock resistance and moisture resistance.
A further object of the present invention is to provide a method of making a semiconductor device using an improved coating material which is suitable for increasing the surface stability of a semiconductor body.